Impairment

Impairment is the objectively measurable reduction in performance on cognitive, psychomotor, or perceptual tasks following substance exposure, regardless of subjective experience. For cannabis, acute impairment affects attention, working memory, reaction time, tracking, divided attention, and executive function; in driving, THC impairs lateral vehicle control and reaction time (Hartman & Huestis 2013 Clin Chem). A 2021 meta-analysis found that impairment on driving-relevant tasks typically resolves within ~5–7 hours after smoked or vaporized THC, though oral THC produces longer impairment (up to 10+ hours) (McCartney et al. Neurosci Biobehav Rev). Blood THC concentration correlates poorly with impairment in frequent users, who show partial behavioral tolerance (Ramaekers 2016). Impairment is the legal and public-health endpoint underlying DUID statutes and workplace testing. Critically, users' subjective feeling of being "sober enough" is an unreliable guide to objective impairment. Citations: Hartman RL, Huestis MA. Clin Chem. 2013;59:478-492; McCartney D et al. Neurosci Biobehav Rev. 2021;126:175-193; Ramaekers JG et al. Sci Rep. 2016;6:26843. ---